Ammonia works well. Remember their sense of smell is virtually an order of magnitude more powerful. Shoot for their nose -- the eyes aren't your target. Any pepper spray works too although you're really upping the ante. Of course if the owners are stupid enough to let their dog run free, well, the dog is going to have to pay for their callousness.

And if a dog does chase you or makes any contact file a complaint immediately. And get treated -- dog bites can get really nasty infections. Cats are worse, but dog bites are bad enough. But file a complaint -- too many laws are being passed now controlling virtually every aspect of dog ownership mostly due to jerks who don't bother training/controlling/spaying/neutering their dogs. People like that shouldn't have dogs in the first place.